Sample handling robots of various configurations are known in the biotechnology industry. A common feature of such systems is the use of a robotic or other motion control device to either move a fluid aspirating/dispensing syringe (herein generally referred to as a sampling probe) about a deck of vessels or other deck components like wash stations, reagent troughs, injection valves, etc., or to move the vessels and/or other deck components relative to a stationary sampling probe. Among the more sophisticated systems, plural sampling probes are ganged together for common movement by a sample handler.
There are two major types of fluidic sampling device designs used on automated liquid handling platforms for metering hundreds of nanoliters to milliliter volumes of liquid samples, reagents, diluents, etc in today's life science industry. Each design type possesses positive and negative attributes that must be weighed against each other when deciding which is better for a particular application.
The first type of design for automated fluidic metering uses a sampling probe remote to the metering device (commonly a stepper driven syringe). A fluidic tube, long enough to permit the probe to freely reach an ensemble of vessels on a robotic deck, is required to connect the probe to the metering device (see FIG. 1). For automated operation, the probe is attached to an X, Y, and Z motion mechanism while the relatively large and heavy metering device remains stationary and fixed to the automation device. In many implementations, a high-speed pumping device is valved between the metering device and probe. This pump is used to quickly wash the probe between uses in order to reduce contamination and carryover.
The most notable disadvantage of this design is that the relatively large fluid volume between the metering device and sampling probe acts as a “fluidic capacitor” causing imprecision in volumetric metering especially when aspirating and dispensing fluids against medium to high pressures. For conventional syringe pumps and tubing volumes used in today's robotic systems, the volumetric uncertainty is in the tens of microliters to hundreds of nanoliters range. This is tolerable when handling volumes in the hundreds of microliters and larger. It is not acceptable for smaller volumes, however as many of today's high-throughput, high technology applications operate in the sub hundred-microliter regime.
The second type of design for automated fluidic metering uses an integrated sampling probe and metering device (see FIG. 2). This overcomes the “fluidic capacitance” problem resulting from the requisite liquid volumes involved with the remote metering/sampling devices described above. Designs of this type are generally capable of delivering against approximately 150 psi.
The disadvantages with this approach are: 1) It is difficult to make the probe small enough to achieve the 9 mm center-to-center spacing preferred by today's high throughput applications; 2) The integrated metering and sampling device has more mass for the gantry to move around resulting in potential speed, accuracy, and precision compromises in the gantry's motion. This is generally overcome by using more robust and higher quality motion equipment, which, unfortunately, also has a commensurate increase in cost; 3) An electrical connection is required to power to the device; and 4) devices having barrel portions small enough to be on 9 mm centers to create an array of fluidic channels connect all the channels to a single platen causing every channel in the array to aspirate and/or dispense the same volume. This is very often an undesirable constraint.